Even vertical spacing in multline and gather environments

Question

Using fractions or expressions with sub- and superscripts may lead to uneven vertical spacing in math environments spanning several lines (i.e., align, gather, multline,...). A fix for align was presented here. Is there a similar solution for multline and/or gather?

This MWE illustrates the problem. The spacing after the first line is larger than after the second due to the sum + subscripts.

\documentclass{scrartcl}
\usepackage{amsmath}

\begin{document}
\begin{minipage}[bt]{0.35\linewidth}
  \begin{multline*}
    x=\sum_{i=1}^nx_n\\
    +y_1+y_2+z_3\\
    +z_1+z_2+z_3
  \end{multline*}
\end{minipage}
\end{document}

Answer 1

It's not related to the problem in the referenced question, there large entries were tight to the surrounding rows and the answer made sure that the spacing strut in those rows was larger than the entry thus preserving row separation but making the row separation more variable. It would not do anything here as the later rows are not large.

Here (I think) you are trying to normalise the distance between baselines not maintain a separation between rows. that would mean analysing all rows of the display which is harder. I'd just use

\setlength\jot{1.5ex} 

or

\begin{spreadlines}{1em} 

from

mathtools